The cutting mechanism in ultraprecision-machining of aluminum single crystals having various orientations using a trial ultraprecision machine was investigated. The (111) plane cutting requires the lowest cutting force and provides the best finished surface roughness among those for (001), (110) and (111) planes. The cutting in the direction of [011] on (111) plane gives the best finished surface roughness .The cutting forces and shear angles were affected by the crystal orientation when the depth of cut was 3 and 4μm. The crystal orientation dependency was not observed at a cutting depth of 1 and 2μm. This is reasonably explained by an affected layer, and this characteristic phenomena is shown in the micro cutting. The cutting force varies when shear strain is less than 3 according to the result on the relation between shear stress and shear strain. The finished surface roughness is affected by the cutting direction, suggesting that the control of the workpiece orientation is effective for improving the working accuracy. Width of lamella on the free surface of chips is affected by the cutting direction and depth of cut.

View full abstract

In order to make clear that the iron compound has some effects on the fracture initiation of Al-Si alloy, microstructure observation has been performed during a tensile deformation using optical microscopy and in-situ scanning electron microscopy. By changing the shape of iron compound from Chinese script type to needle-like one, we can achieve higher ductility, while the ultimate tensile strength decreases. Needle-like and massive type iron compounds are cracked easily at the ealier stage of deformation. In comparison with the needle-like compound, the Chinese script compound can hold the higher stress. When the form of iron compounds was changed, the initiation of crack occurred not at the silicon particles but at the iron compounds.

View full abstract

Reheating and isothermal holding was carried out using strained bulk, briquet and chip in order to get fine solid particle. Furthermore, semi-solid stirring was conducted employing chips, with fine solid particles during isothermal holding. Magnesium solid solution (α-phase) in each raw material recrystallizes on reheating and then melting occurs at interface between α-phase and eutectic compound, and recrystallized grain boundary below holding temperature. At isothermal holding temperature, solid particles break up nearly perfectly, and are finer spherical particles than those of commercial bulk sample. The spherical solid particle coarsens in proportion to cube root of holding time. From analyses of distribution form of solid particle diameter, it is clear that contribution of coalescence to the particle growth decreases and that of Ostwald ripening increases with the lapse of time. When chip sample is stirred, solid particle size is a half of that of bulk sample and the volume fraction of liquid phase increases. Moreover, growth of the solid particle is little even though stirring temperature raises. Amount of liquid phase increases and the fluidity of slurry improves with the increase of holding temperature.

View full abstract

Alumina short fiber/AZ91D magnesium alloy composites are fabricated using a squeeze casting method. In this study, the effect of the graphite lubricant on the preform deformation was investigated. Additionally, macro- and microstructures and mechanical properties of the composites fabricated at the optimum condition are investigated. The preform deformation is caused by the α phase that crystallizes near the surface of a die. Namely, the primary α phase accumulates on the preform and disturbs the molten metal infiltration during squeeze casting. As the result, high compressive pressure acts on the preforms and causes the preform deformation. The coefficient of heat transfer becomes a small value by coating the graphite lubricant on the inside of a die. In this case, no α phase crystallizes near the surface of a die before squeeze casting. Therefore, the preform deformation does not occurs. The composites have high tensile strength at the elevated temperature. But the elongation of the composites is very small at temperatures between room temperature and 250°C. The T6 treatment improves tensile strength of the composites at room temperature. However, as tensile test temperature raises, the effect of the T6 treatment decreases and subsequently tensile strength of T6- treated composites is approximately equal to that of as-cast composites at 250°C.

View full abstract

Electrical resistivity of Mg-Al binary alloys containing up to 14.2%Al has been measured at 77K and 300K. Resistivity of alloys containing up to 9.69%Al, which give perfect solid solution after appropriate solution treatments, shows a good linear relation with a function g(X) = X (1-2.86X) of aluminium atomic fraction X deduced by an empirical correction of Nordheim's rule. The resistivity at 300K and 77K can be expressed as,
44<ρ^Mg-Al₃₀₀/nΩm=_??_1.966×10³X(1-2.86X)+44.73_??_± 1.2<175
5<ρ^Mg-Al₇₇/nΩm=_??_2.095×10³X(1-2.86X)+5.46_??_± 1.0<142.
From gradients Δρ^g(X) of these linear relations, η^Mg = Δρ₃₀₀/Δρ₇₇ is determined to be 0.938 and the deviation from Matthiessen's rule (DMR) is negative in agreement with previous reports on alloys up to 2.8%Al. Relation between R = ρ₃₀₀/ρ₇₇ and ρ₇₇ corrected with the DMR is obtained as
5<ρ^Mg-Al₇₇/nΩm=_??_39.53/(R-0.938)+0.175_??_± 1.0<142
for change in concentration of solute aluminium in Mg-Al solid solution.
dρ/dT measured between 280K and 308K decreases with aluminum concentration, which also coincides with the negative DMR of solute aluminum. The R of two (α + β) phase specimens shows a tendency to increase with volume fraction of β (Mg₁₇Al₁₂) phase.

View full abstract